Apple - How to show the map in Photos?
For more recent versions of Photos.app (Version 2.0 that came with macOS 10.12 Sierra at least), there is a "Places" item avaialble under "Albums" in the sidebar (use "View" -> "Show Sidebar" if it is not visible). This gives a map view similar to that available in iPhoto.app.
For older versions of Photos.app, it does not appear that there is a way to see ALL photo locations on a map at one time, aside from a small Info window. Here's what you need to do:
For the small info window that shows all locations:
1. Go to the Albums tab in Photos
2. Right-click on "All Photos" -> Get info
3. Note the small window has a map included which you can zoom in/out of
For maps that vary by date:
- Go to View menu -> Metadata -> Location
Go to the Photos tab and zoom all the way out to Years
Note that there are locations next to the year. Click on the location name
You can type a location into the search box and one of the options usually is a location; if you select it, a map comes up showing all of the photos taken in that location. For example, if you type 'Colorado' in the search box, 'Colorado - State' is one of the choices.